The present invention relates to a lens antenna used with millimetric wave radar, etc. for mobile units such as vehicles.
Radar systems for mobile units such as vehicles, e.g., cars and motorcycles are now under extensive investigations for the purpose of automatic navigators, risk managements, etc. Among others, radar harnessing waves in the so-called millimetric wave range enables associated systems to be easily reduced in size and weight, and so is suitable for use on mobile units.
This radar system is generally broken down into a millimetric wave subsystem including oscillators, amplifiers, etc. and an antenna. Promising for this antenna is a lens antenna because it is relatively simple in structure and control of its directivity, etc. is achievable with relative ease.
The lens antenna itself has been investigated from various point-of-views as typically set forth in JP-A""s 51-100664 and JP-B 59-23483.
A conventional lens antenna is generally made up of a body of rotation, as in optical glass, with one surface being of geometrical shape such as plane, sphere, hyperboloid, and paraboloid, and the other surface being of quasi-optically determined shape in consideration of the performance in demand, etc.
However, when the antenna in the form of a body of rotation is mounted on the surface of a mobile unit, there is no option but to locate the antenna on the center axis of the mobile unit so as to reduce damage to the external design thereof as much as possible. This is because most of mobile units are horizontally symmetric. Moreover, since the antenna formed on the body of rotation is also vertically symmetric, the vertically and horizontally symmetric portion of the surface of the associated mobile unit, especially an automobile is defined by a very limited portion, for instance, the leading portion of the center of a bumper, as shown at a position F in FIG. 8 as an example. In most cases, however, the geometrical radiation-side surface is in no coincidence with the surface shape that forms the surface of a bumper or the like of the mobile unit such as a vehicle. Thus, an element of an incompatible design located on the surface of the mobile unit is a chief factor for noticeable damage to the appearance thereof.
In particular, this poses a grave problem to a mobile unit such as an automobile in which design preferences are incorporated with importance attached to its appearance.
Further, when a mobile unit moving at high speed has a portion deformed slightly from the ideal configuration given by hydrokinetics, this portion becomes a factor for a lowering of the motion performance of the mobile unit due to large resistance occurring during high-speed movement. As is the case with a body structure excelling in aerodynamic properties, which is now intensively studied in the field of motorcars or motorcycles, therefore, the location of a structure that projects from or deforms the surface configuration of the mobile unit must be avoided as much as possible.
For an antenna capable of giving a free surface configuration conforming to the surface configuration forming the surface of a mobile unit, a conformal array antenna or the like is now under investigations, for instance, in the field of aviation equipments. However, the arrangement of a number of minute elements runs counter to cost reductions. In addition, the directivity performance obtained by control of a number of such elements is dynamically less than satisfactory.
Thus, to shelter this lens antenna with a resin radome is envisaged. However, the formation of the resin radome using a material having improved millimetric wave properties incurs an increase in the number of additional steps, which is a factor for further cost increases, and is unsuitable for general customer-oriented, mass-produced vehicles, and so on. Another possible approach is to house a lens antenna within a mobile unit as shown typically at a position I in FIG. 8, which lens antenna is a body of rotation and so does not square with the external shape of the mobile unit. However, reflections and attenuations due to the exterior materials of the mobile unit make it difficult to obtain the desired performance.
JP-A 08-139514 discloses a lens antenna integrated with a vehicle""s bumper. In the structure shown in this publication, however, a convex lens antenna is formed on the back side of the bumper by means of integral molding or a plano-convex lens antenna is located on the back side of the bumper, as typically shown at a position H in FIG. 8, so that waves passing through the lens antenna portion can also propagate through the bumper. However, it is difficult to obtain a bumper body, for which low-cost material is required on the premise of recycling and which is exposed to mechanical stresses, and a lens antenna required to have a high degree of millimetric wave properties and a quasi-optical function as well as a shape with high dimensional accuracy, using the same material and integral molding.
For this reason, waves are affected by the quasi-optical refractive index given by the shape defined by the bumper portion and the lens antenna portion, and so it is difficult to obtain the desired performance. In addition, the location of the plano-convex lens on the back side of the bumper structurally gives rise to a junction or gap at which reflections or attenuations occur, resulting in a difficulty in obtaining the desired performance.
Yet possible approach is to use resin for a number plate and allow a part thereof to operate as an antenna, as shown at a position G in FIG. 8 and set forth in JP-A 07-283634. However, the replacement of number plates themselves is not realistic because of an enormous number of vehicles needing number place replacement and some considerable alternation of control of number plates themselves.
U.S. Pat. Nos. 4,224,626 and 4,847,628 disclose an aspherical lens antenna. However, although both publications show improvements in F-number, frequency properties and directivity, they teach nothing about the use of the lens antenna on a mobile unit and the compatibility of the lens antenna with the shape of the surface of an asymmetric mobile unit.
U.S. Pat. No. 5,264,859 discloses a lens antenna for radar used on mobile units. As in the aforesaid publications, this publication shows nothing about the compatibility of the lens antenna with the asymmetric configuration and the surfaces of mobile units.
An object of the present invention is to achieve a high-performance lens antenna which can be integrated with the external (surface) shape of a mobile unit with no damage to the appearance of the mobile unit, is easy to manufacture and assemble at relatively low costs as well as a lens antenna array comprising a plurality of such lens antennas.
The aforesaid object is achieved by the following embodiments.
(1) A lens antenna mounted on a mobile unit, which is in a non-body of rotation form, and in which, at a lens antenna-mounted position, the direction and magnitude of inclination and curvature of the surface of the mobile unit as well as the direction and magnitude of inclination and curvature of a radiation-side surface of the lens antenna are within xc2x120%, and a focal-side surface of the lens antenna is formed with respect to the radiation-side surface in such a way that the radiation-side surface and the focal-side surface have a quasi-optical configuration as a lens antenna.
(2) The lens antenna of (1), which is formed of a resin material or ceramics.
(3) The lens antenna of (1), wherein a constituting material thereof has a specific dielectric constant of ∈r=2 to 12 in a frequency range used.
(4) The lens antenna of (1), wherein a focal length thereof is ⅓ to 3 times as large as a maximum length of an aperture projection surface thereof.
(5) The lens antenna of (1), wherein a junction of a surface of said mobile unit body and a surface of said lens antenna forms a continuous surface.
(6) The lens antenna of (1), wherein at least the radiation-side surface thereof is colored.
(7) The lens antenna of any one of (1) to (6), which is used in a frequency range of 30 to 300 GHz.
(8) The lens antenna of any one of (1) to (7), which has an antireflection film on the radiation-side surface thereof.
(9) The lens antenna of any one of (1) to (8), wherein the aperture projection surface thereof is of an elliptical shape.
(10) The lens antenna of any one of (1) to (8), wherein an auxiliary reflector, an auxiliary lens or a radio prism is located on a wave path between the lens antenna and a primary radiator.
(11) The lens antenna of any one of (1) to (10), wherein a plurality of lens antennas, each as recited in any one of (1) to (10), are integrally formed.